Lambda Parallel Research Articles

Workspace and kinematic structure analysis of a 6-DOF Lambda parallel kinematic machine

This paper presents workspace and kinematic analysis of a parallel kinematic machine based on the Lambda mechanism. The considered parallel kinematic machine has six degrees of freedom (DOF), achievable with six actuated translation joints. The kinematic analysis includes the definition of every active part of the machine, as well as the definition of every active or passive joint used to connect machine parts. The mathematical model of the machine is created for the better understanding of the machine's operation. The proposed mathematical model of the machine includes inverse kinematic equations, whose solving presents the first step in workspace analysis. In this case, the offered parallel kinematic machine has six active-joint variables, and every active-joint variable is the result of one inverse kinematic equation. Verification of the inverse kinematic equations has been done analytically, using MatLab software and a CAD/CAM system. Workspace analysis, as one of the most important parameters of the parallel kinematic machine, presents the main topic of this paper. In this case two approaches to the workspace analysis are given. The first considered analysis is used to determine the achievable workspace of the machine, and the second analysis is used to determine the total orientation workspace of the machine. Polar coordinates are used to simplify the process of the workspace analysis.

Diffusion tensor imaging detects axonal injury and demyelination in the spinal cord and cranial nerves of a murine model of globoid cell leukodystrophy

Globoid cell leukodystrophy is an inherited neurodegenerative disorder caused by a deficiency of the lysosomal enzyme galactosylceramidase. In both human patients and the authentic murine Twitcher model, pathological findings include demyelination as well as axonal damage in both the central and peripheral nervous system. Diffusion tensor imaging (DTI) has emerged as a powerful noninvasive technique that is sensitive to these white matter disease processes. Increases in radial diffusivity (lambda perpendicular) and decreases in axial diffusivity (lambda parallel) correlate with histopathological evidence of demyelination and axonal damage, respectively. Compared to age-matched, normal littermates, DTI of optic nerve and trigeminal nerve in end-stage Twitcher mice displayed a statistically significant increase in lambda perpendicular and decrease in lambda parallel, consistent with previously characterized demyelination and axonal damage in these regions. In the Twitcher spinal cord, a statistically significant decrease in lambda parallel was identified in both the dorsal and ventrolateral white matter, relative to normal controls. These results were consistent with immunofluorescence evidence of axonal damage in these areas as detected by staining for nonphosphorylated neurofilaments (SMI32). Increase in lambda perpendicular in Twitcher spinal cord white matter relative to normal controls reached statistical significance in the dorsal columns and approached statistical significance in the ventrolateral region. Correlative reduced levels of myelin basic protein were detected by immunofluorescent staining in both these white matter regions in the Twitcher spinal cord. Fractional anisotropy, a nonspecific but sensitive indicator of white matter disease, was significantly reduced in the optic nerve, trigeminal nerve, and throughout the spinal cord white matter of Twitcher mice, relative to normal controls. This first reported application of spinal cord DTI in the setting of GLD holds potential as a noninvasive, quantitative assay of therapeutic efficacy in future treatment studies.

Diffusion tensor imaging of the auditory pathway in sensorineural hearing loss: Changes in radial diffusivity and diffusion anisotropy

To prospectively compare diffusion tensor imaging (DTI) measures of axial diffusivity (lambda parallel), radial diffusivity (lambda perpendicular), mean diffusivity (MD), and fractional anisotropy (FA) along the auditory pathway of patients with sensorineural hearing loss (SNHL) and normal controls. In 37 individuals with SNHL and 10 healthy controls, two regions of interest (ROIs) positioned along the auditory pathway-the lateral lemniscus (LL) and the inferior colliculus (IC)-were investigated bilaterally using diffusion tensor imaging at 3 T. SNHL patients were divided into three groups: patients with bilateral hearing loss, patients with unilateral hearing loss, and patients with partial hearing loss. DTI measures (lambda parallel, lambda perpendicular, MD, FA) of both ROIs were determined in all subjects. The FA value was reduced and the lambda perpendicular was increased both at the lateral lemniscus and the inferior colliculus of patients with SNHL compared with controls. Similar changes were seen between the ipsilateral and contralateral LL and IC for patients of unilateral profound hearing loss. No changes were observed in any other parameters. In SNHL patients DTI showed a high radial diffusivity that consequently led to a decreased fractional anisotropy in the LL and the IC.